Preheat oven to 200°C. Heat the onions in a 28cm (with a heatproof handle) frying over low heat. Add the butter and oil and cook gently for 15 minutes.

Step 2

Gently fold through the thyme and cook for 15 minutes or until the onions are soft and golden. Sprinkle with the brown sugar. Add the balsamic vinegar. Cook for 1-2 minutes until the vinegar reduces. Season with salt and pepper.

Step 3

Working quickly, lay the puff pastry over the onions. Fold back the edges. Place the frying pan in the oven and bake for 20 minutes or until the pastry is puffed and golden. Turn the tart out onto a large serving plate. Top with the rocket and goats cheese. Drizzle over the extra balsamic vinegar to serve.